1. Field of the Invention
The present invention relates to a fuel supply system including a fuel pump which uses an internal combustion engine as a motive power source.
2. Description of the Related Art
Conventionally, as a fuel supply system of this type of an internal combustion engine, one disclosed in Japanese Laid-Open Patent Publication No. 2005-307747, for example, is known. This conventional fuel supply system includes a fuel pump and an electromagnetic valve. The fuel pump includes a plunger abutting a driving cam which uses the engine as the motive power source, and the plunger is driven by the driving cam whereby fuel is discharged to a fuel injection valve side. The amount of the discharge of fuel is controlled by controlling an energization time period of the electromagnetic valve. Further, in the conventional fuel supply system, an attachment error between the driving cam and the fuel pump is estimated, and the energization time period is corrected based on the estimated attachment error so as to properly control the amount of fuel to be discharged via the electromagnetic valve. Further, calculation of the energization time period described above is executed at a timing (hereinafter referred to as “predetermined crank angle timing”) which corresponds to a predetermined crank angle position of the engine.
In the fuel supply system including the fuel pump and the electromagnetic valve, described above, generally, a target value of the amount of fuel to be discharged from the fuel pump is calculated according to operating conditions of the engine, and the energization time (timing or time period) of the electromagnetic valve is calculated according to the calculated target value of the amount of fuel to be discharged and a parameter for control such as fuel pressure. In this case, with a view to properly controlling the amount of fuel to be discharged from the fuel pump, it is desirable that the calculation of the energization time is executed in such an appropriate timing (hereinafter referred to as “proper calculation timing”) that the calculation is executed according to the newest control parameter and the energization of the electromagnetic valve is positively completed within the calculated energization time period. Further, since fuel is discharged by driving the plunger of the fuel pump using the driving cam, this proper calculation timing is generally corresponds to a predetermined rotational angle position of the driving cam, within a predetermined time period preceding and following a timing at which a top of a cam nose of the driving cam is abutting the plunger, inclusive of the timing. On the other hand, the predetermined crank angle timing mentioned above sometimes misses the proper calculation timing, depending on specifications of design of the engine.
On the other hand, in the conventional fuel supply system described above, the calculation timing of the energization time period of the electromagnetic valve is merely set to the predetermined crank angle timing. Therefore, when the predetermined crank angle timing misses proper calculation timing as described above, the calculation of the energization time period cannot be executed at the proper calculation timing. As a consequence, the calculation of the energization time period according to a newer parameter for control cannot be performed, and the energization of the electromagnetic valve cannot be completed within the calculated energization time period, and in turn, there is a fear that the amount of fuel to be discharged from the fuel pump cannot be properly controlled.